On the corrections to Dashen's theorem

The electromagnetic corrections to the masses of the pseudoscalar mesons \pi and K are considered. We calculate in chiral perturbation theory the contributions which arise from resonances within a photon loop at order O(e^2 m_q). For the corrections to Dashen's theorem we find rather moderate deviations in discrepancy to the values found in the literature

On the Corrections to Dashen's Theorem

The electromagnetic corrections to the masses of the pseudoscalar mesons $\pi$ and $K$ are considered. We calculate in chiral perturbation theory the contributions which arise from resonances within a photon loop at order $O(e^2 m_q)$. Within this approach we find rather moderate deviations to Dashen's theorem.Comment: 14 pages, sligthly enlarged version; a numerical error is corrected and the embedding of the figures is improved. The complete paper, including figures, is also available via anonymous ftp at ftp://www-ttp.physik.uni-karlsruhe.de/ , or via www at http://www-ttp.physik.uni-karlsruhe.de/cgi-bin/preprints/; to be published in Phys.Rev.

Who wants to conserve remaining forest fragments in the Manompana Corridor?

Contiguous forests in Madagascar are continuously converted into forest fragments due to deforestation, and dispersed into landscape mosaics dominated by agriculture. These fragments are of increasing importance for biodiversity conservation as well as for the well being of rural inhabitants, providing a high diversity of timber and non- timber forest products. An increasing number of international projects are therefore trying to preserve remaining forests and to transfer the management of these forests to local communities. However, it is not known how important the preservation of forest fragments is to local people. We therefore explore the importance of forest fragments as a source of cash income to different groups separated by wealth level and access to forest resources. A multi-method research approach was taken, based on score application exercises as well as interviews with individual households and focus groups. Our study site was located at the east coast of Madagascar in the Manompana corridor. Results show that some groups are significantly more interested in the preservation of forest fragments than others. Interest is significantly related to the wealth of local inhabitants as well as to the walking distance between villages and forest resources. Nevertheless, interest in resource preservation does not depend on how important fragments are to local people, but rather on the awareness about resource scarcity.  Résumé En raison d’une forte déforestation sur la côte est de Madagascar, de nombreux massifs forestiers d’un seul tenant et de vastes écosystèmes interconnectés ont été détruits, laissant des fragments de forêts qui s’intègrent dans une mosaïque paysagère dominée par l’agriculture. Ces fragments gagnent en importance. Ils jouent un rôle de premier plan dans les réseaux de biodiversité en assurant un certain niveau de connectivité. Mais les fragments sont essentiels au bien - être de la population locale, fournissant produits et services pour la consommation quotidienne ou donnant accès à un revenu monétaire. Sur un plan global, aussi bien les organisations de protection de la nature que les milieux scientifiques essayent d’endiguer la déforestation. Depuis les années 1996 la politique nationale à Madagascar a généré lois et processus visant à transférer la gestion des ressources forestières de l’Etat aux communautés locales. Cependant, il n’a pas été possible, jusqu’à ce jour, d’atténuer l’ampleur de la destruction et de la fragmentation des forêts pluviales de l’île. Plus encore, à l’heure actuelle la perception de l’importance des fragments de forêts n’est pas connue par la population. Un projet de recherche a été lancé pour contribuer à combler cette lacune, dans le corridor de Manompana, sur la côte. Les buts de ce projet étaient (i) d’explorer l’importance des fragments de forêts pour les revenus monétaires de la population locale et (ii) d’analyser la perception de l’importance des fragments de forêts par la population locale. Les recherches se sont déroulées dans quatre villages situés à des distances différentes du grand massif forestier. La population locale a été répartie en différentes catégories de niveau de vie et en fonction de la distance à parcourir entre les villages et la forêt. Cette approche a permis d’étudier le rôle de la forêt quant aux revenus monétaires des différents groupes de la population. Nous avons également cherché à établir un lien entre l’ampleur des revenus monétaires et un intérêt à conserver les fragments de forêts qui subsistent. Nos méthodes de recherche font recours à des exercices de « scoring », à des discussions avec des groupes ciblés et à des enquêtes de ménages. Il ressort des analyses que certains groupes ont un intérêt à conserver les fragments forestiers. Cet intérêt est significativement lié, d’une part, au niveau de vie de la population, d’autre part, à la distance entre le village et le massif forestier. Cependant, l’intérêt à conserver les fragments de forêts est plus fortement lié à la conscience de la finitude des ressources forestières qu’au montant des revenus monétaires que la population peut tirer des produits forestiers.

Baryon chiral perturbation theory with virtual photons and leptons

We construct the general pion-nucleon SU(2) Lagrangian including both virtual photons and leptons for relativistic baryon chiral perturbation theory up to fourth order. We include the light leptons as explicit dynamical degrees of freedom by introducing new building blocks which represent these leptons.Comment: 11 page

On the extraction of the quark mass ratio (m_d - m_u)/m_s from Gamma(eta' -> pi^0 pi^+ pi^-)/Gamma(eta' -> eta pi^+ pi^-)

The claim that the light quark mass ratio (m_d - m_u)/m_s can be extracted from the decay width ratio Gamma(eta' -> pi^0 pi^+ pi^-)/Gamma(eta' -> eta pi^+ pi^-) is critically investigated within a U(3) chiral unitary framework. The influence of the recent VES data on the eta' -> eta pi^+ pi^- decay is also discussed.Comment: 9 pages, 1 figure, 6 table

Solving correlation clustering with QAOA and a Rydberg qudit system: a full-stack approach

We study the correlation clustering problem using the quantum approximate optimization algorithm (QAOA) and qudits, which constitute a natural platform for such non-binary problems. Specifically, we consider a neutral atom quantum computer and propose a full stack approach for correlation clustering, including Hamiltonian formulation of the algorithm, analysis of its performance, identification of a suitable level structure for ${}^{87}{\rm Sr}$ and specific gate design. We show the qudit implementation is superior to the qubit encoding as quantified by the gate count. For single layer QAOA, we also prove (conjecture) a lower bound of $0.6367$ ($0.6699$) for the approximation ratio on 3-regular graphs. Our numerical studies evaluate the algorithm's performance by considering complete and Erd\H{o}s-R\'enyi graphs of up to 7 vertices and clusters. We find that in all cases the QAOA surpasses the Swamy bound $0.7666$ for the approximation ratio for QAOA depths $p \geq 2$. Finally, by analysing the effect of errors when solving complete graphs we find that their inclusion severely limits the algorithm's performance.Comment: 22 + 11 page

Film Edge Nonlocal Spin Valves

Spintronics is a new paradigm for integrated digital electronics. Recently established as a niche for nonvolatile magnetic random access memory (MRAM), it offers new functionality while demonstrating low power and high speed performance. However, to reach high density spintronic technology must make a transition to the nanometer scale. Prototype devices are presently made using a planar geometry and have an area determined by the lithographic feature size, currently about 100 nm. Here we present a new nonplanar geometry in which one lateral dimension is given by a film thickness, the order of 10 nm. With this new approach, cell sizes can shrink by an order of magnitude. The geometry is demonstrated with a nonlocal spin valve, where we study devices with an injector/detector separation much less than the spin diffusion length.Comment: 10 pages, 3 figure